To write the book he researched why there were so many serial killers between 1950 and 2000. It is mentioned in the article from the New York Post and from Vronsky's book that there was a “hidden surge of war-traumatized fathers” returning home which created the next generation of murderers. Check out the quote below of what exactly influenced these killers.

When men came back from the Vietnam War, within several years after that, we had diagnosed post-traumatic stress disorder. But nothing of that was available to these men coming back from the Second World War and they had to essentially suck it up — they were tossed the G.I. Bill, told to go to college and forget about it. And so the more I explored the children of World War II veterans, this notion appeared of their fathers returning in this sullen silence from the war and never speaking about it — this kind of brooding shadow — I began to realize that if this is the case with healthy individuals, imagine the fathers of those who became serial killers.

If Vronsky's theory holds any weight of truth, then we can expect another generation of serial killers in the future. This is based off of the stress on people during the financial crisis back in 2008. To find out more about Vronsky's theory click here.